1. Field of the Invention
This invention relates to computer systems in general, and more particularly to externally managing frozen file images in shared storage environments utilizing sparse data objects.
2. Description of the Related Art
Modern storage environments may include many interconnected storage objects. The interconnection network is the physical-layer network technology that provides the infrastructure to connect the various elements of a shared storage environment. Within the shared storage environment, file system abstractions may be built on top of logical volumes that may themselves be distributed across multiple storage devices. As the number of logical volumes and file system abstractions grows, the complexity of the entire storage environment grows dramatically.
To limit bottlenecking and improve data throughput, distributed shared storage environments may separate the actual storage of data from the management of that data. Storage architectures that employ this technique may be referred to as out-of-band or asymmetric systems. A metadata server (MDS) may provide higher-level data management functions including, among others, file system mapping, data mirror synchronization, client authentication and access privileges. The data itself is generally stored on various storage devices attached to the network. Without the need to worry about providing file system abstractions, or other metadata, storage devices may focus on provide only data storage and retrieval functionality. Object-based storage devices (OBSDs) are one example of the type of storage devices that may be employed in out-of-band or asymmetric systems.
Client nodes initially contact the MDS to request access to a specific dataset. The MDS, after authenticating the client node and applying whatever access policies are in place, generally provides the requesting client node with information (metadata) about where that particular dataset is stored, and an access token to present to the actual storage device. Client nodes may then communicate directly with storage devices, presenting the access token for reading and writing of data. The access token tells the storage device what data the client node is allowed to access, and also whether that client is allowed read/write access, or merely read-only access.
This separation of data from its associated authentication and metadata management can allow the actual data traffic to be routed around the MDS, thus preventing the MDS from becoming a bottleneck and limiting data throughput. This may also allow the MDS to be optimized for metadata lookups which may involve smaller reads and writes, while allowing the storage devices to be optimized for bulk data transfer of block reads and writes.
In distributed file systems where multiple client nodes may simultaneously access the same data, files may be fixed into specific versions to ensure data integrity among client sessions. These dataset versions may be referred to as file images.